This invention relates to a regeneratively-operated coke oven having means for supplying non-preheated gas to the heating flues wherein such means includes a smooth and pore-free surface to prevent accretion of carbon which precipitates from rich gas conducted along a high-temperature surface.
Dry distillation gas produced in a coke oven during the course of a coking process includes a substantial portion of methane. This gas is frequently used for heating the coke ovens. The temperature of the regions of rich gas burners in the heating flues of coke ovens is always higher than 1000.degree. C. during operation of the oven. The temperature may reach 1500.degree. C. to 1600.degree. C. in the regions of rich gas burners for coke ovens to carry out short coking times of, for example, fourteen hours. In some instances, rich gas is used which, like residual synthesis gas, has a higher hydrocarbon content than the distillation gas. When such rich gases are supplied to the heating flues of coke ovens, carbon is precipitated from the gas on the surface of the burners disposed in the heating flues. The present invention is based on the fact that at temperatures in the range of 1000.degree. C. to 1600.degree. C. methane and its homologues have a tendency to dissociate into carbon and hydrogen constituents. The carbon precipitate gradually hardens and transforms into graphite which reduces the cross-sectional areas of the openings in the burners. Particularly thick graphite accretions are formed in the burners which extend far, e.g., 1 meter and more, into the heating flues.
It is a common practice in the regenerative operation of coke ovens to prevent blockage of the burners by introducing air into the rich-gas ducts. The air is used for the purpose of degraphitizing during the particular regenerative hot cycle during which no gas is supplied to the heating flues and the chimney draft which acts on the heating flues is frequently regarded as sufficient for drawing the air into the flues. In some instances, the air for degraphitizing is supplied under pressure into the heating flues. Air has also been introduced into an inoperative burner in a heating flue while gases are burning upwardly in the flue which is possible when several burners are provided in one heating flue. A small quantity of air has also been continuously added to the gas which is supplied to the heating flues. This addition of air to the gas occurs at a point immediately prior to the entry of the gas into the heating flue in order to restrict the precipitation of graphite from the gas.
The air intended for degraphitizing is discharged into the bottom end of a heating flue where a downward combustion occurs in the flue. The discharging of air into the flue increases the air content of the gaseous product flowing to the chimney in the course of the combustion process. The combustion process occurring in the heating flues must be carried out with an excess of air in order to insure complete combustion of the fuel gas. Additional heat must, therefore, be generated for heating the degraphitizing air in the gas supply ducts. This increases the heat comsumption of the coke oven. On the other hand, if insufficient air is supplied to the heating flues, there is a risk of a breakdown of an oven operation because the ducts and burners become increasingly blocked with graphite.